The present invention relates to a novel method for the preparation of an alkynyl compound. More particularly, the invention relates to a novel synthetic method for the preparation of various kinds of alkynyl compounds useful as an intermediate of various organic compounds used as agricultural chemicals or, in particular, sex pheromones of insect pests, in which the desired alkynyl compound can be obtained without isolating the intermediate product in the successive steps of reactions.
In the prior art, a long-chain alkynyl compound is usually synthesized by a method in which the chain length of the alkynyl group of the starting alkynyl compound is extended by adding a chain segment of a desired length to each side of the triple bond separately from the other side. This conventional method, however, has a disadvantage that the yield of the desired compound cannot be high enough for the reasons that the synthetic process is lengthy and complicated because the chain extension must be undertaken separately at both sides of the triple bond of the starting alkynyl compound, that the functional groups must be protected by a protective group which must be subsequently eliminated, that the reaction sometimes must be performed at a high temperature under a superatmospheric pressure or at a low temperature in order to impart the reactive site of the starting compound with selectivity for the desired reaction and so on.
For example, Japanese Patent Kokai 57-24392 teaches a method for the synthesis of cis-13-octadecen-3-yn-1-ol of the formula HO(CH.sub.2).sub.2 C.tbd.C(CH.sub.2).sub.6 R, in which R is cis-3-octenyl group, as an intermediate for the synthesis of the sex pheromone of a notorious pest Synanthedon hector. The synthetic method thereof is a two-step process consisting of the first reaction of 8-bromo-1-octyne with cis-3-octenyl magnesium chloride to form cis-11-hexadecen-1-yne of the formula HC.tbd.C(CH.sub.2).sub.6 R, which is then reacted in the second step reaction with methyl magnesium chloride and ethylene oxide to give the desired product. The reactions must be conducted at a low temperature and the overall yield of the desired product is not high enough with the partial yields in the first step and second step reactions of 60% and 90%, respectively.
Thus, it is eagerly desired to develop an efficient method for the synthetic preparation of a long-chain alkynyl compound in a relatively simple process which can be performed without chilling the reaction mixture or requiring other special reaction conditions but still give the desired product in a high yield.